Can you get a soft tissue sarcoma without a lump as a symptom?

Yes, internally: Soft tissue sarcomas can occur in the abdomen where you would not feel a lump because it is too deep.

Yes: Most sarcomas are on the skin or in the arms and legs, but some cannot be felt because they are too deep, aren't large enough, are just skin nodules, or are growing in deeper areas of the body, like muscles in the abdomen or the fat behind the intestines (retroperitoneum).

Yes, but rarely: If the sarcoma is hidden by normal tissues, you will not feel a lump. For example in the thigh, where there are lots of muscles, the sarcoma will not be felt until it is quite large. In the pelvis, it is even worse. The sarcoma may be picked up incidentally if imaging is done for other reasons. If the sarcoma affects nerves or vessels, it may present itself due to pain before a mass is felt. Otherwise, most sarcomas are painless.